Division by zero in TFLite's implementation of `OneHot`

Impact

The implementation of the OneHot TFLite operator is [vulnerable to a division by zero error](https://github.com/tensorflow/tensorflow/blob/f61c57bd425878be108ec787f4d96390579fb83e/tensorflow/lite/kernels/one_hot.cc#L68-L72):

```cc

int prefix_dim_size = 1;

for (int i = 0; i < op_context.axis; ++i) {

prefix_dim_size *= op_context.indices->dims->data[i];

}

const int suffix_dim_size = NumElements(op_context.indices) / prefix_dim_size;

`

An attacker can craft a model such that at least one of the dimensions of indices would be 0. In turn, the prefix_dim_size value would become 0.

Patches

We have patched the issue in GitHub commit [3ebedd7e345453d68e279cfc3e4072648e5e12e5](https://github.com/tensorflow/tensorflow/commit/3ebedd7e345453d68e279cfc3e4072648e5e12e5).

The fix will be included in TensorFlow 2.5.0. We will also cherrypick this commit on TensorFlow 2.4.2, TensorFlow 2.3.3, TensorFlow 2.2.3 and TensorFlow 2.1.4, as these are also affected and still in supported range.

For more information

Please consult [our security guide](https://github.com/tensorflow/tensorflow/blob/master/SECURITY.md) for more information regarding the security model and how to contact us with issues and questions.

Attribution

This vulnerability has been reported by members of the Aivul Team from Qihoo 360.